lai (yl8859) – HW20 – Ross – (15200)1Thisprint-outshouldhave7questions.Multiple-choice questions may continue onthe next column or page – find all choicesbefore answering.00110.0 pointsA distant star has a single planet circling it ina circular orbit of radius 7.11×1011m. Theperiod of the planet’s motion about the staris 703 days.Whatisthemassofthestar?Thevalue of the universal gravitational constantis 6.67259×10-11N·m2/kg2.Correct answer: 5.76416×1031kg.Explanation:Let :G= 6.67259×10-11N·m2/kg2,RB= 7.11×1011m,andTB= 703 day.TB= (703 day)parenleftbigg24 h1 dayparenrightbigg3600 s1 h= 6.07392×107s.According to Newton’s explanation of Ke-pler’s third lawR3BT2B=G Ms4π2=const.The mass of the star is thusMs=4π2GR3BT2B=4π26.67259×10-11N·m2/kg2×(7.11×1011m)3(6.07392×107s)2=5.76416×1031kg.00210.0 pointsAn object is dropped from rest from a height6.9×106m above the surface of the earth.If there is no air resistance, what is its speedwhen it strikes the earth?The accelerationof gravity is 9.81 m/s2and the radius of theEarth is 6.37×106m.Correct answer: 8.06136 km/s.Explanation:Let :h= 6.9×106m,g= 9.81 m/s2,andr= 6.37×106m.

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